Novel quantitative trait loci identified for bean rust and the fuscan subspecies of common bacterial blight in an F2 tepary bean population.

Bean rust, caused by Uromyces appendiculatus, is one of the most critical diseases affecting common bean (Phaseolus vulgaris L.) worldwide. Similarly, common bacterial blight, caused by Xanthomonas fuscans subsp. fuscans (Xff) and Xanthomonas axonopodis pv. phaseoli (Xap), poses major threats to common bean production globally. While common bean exhibits limited natural resistance to these pathogens, tepary bean (Phaseolus acutifolius A. Gray), a closely related species, has shown resistance to both rust and common bacterial blight. This study aimed to identify tepary beans resistant to rust and Xff, to pinpoint genomic regions controlling this resistance. Twenty-three tepary bean genotypes were inoculated with multiple rust races and Xff isolates. Several tepary genotypes exhibited immunity to eight rust races, and a few were also resistant to two isolates of Xff. An F2 biparental tepary bean population was developed from one resistant and one susceptible genotype to map quantitative trait loci (QTLs) for resistance to these pathogens. The population was phenotyped by inoculating with two rust races and a mixture of two isolates of Xff. Genotyping by sequencing was employed to genotype the biparental population. A major QTL for the rust pathogen was identified on chromosome Pa10, and a major QTL for common bacterial blight fuscans was identified on chromosome Pa07. Neither of these QTLs have been previously reported in common bean, suggesting that tepary bean possesses different genes controlling the resistance to both pathogens. Both tepary genes should be considered for introgression into common bean through interspecific crossing.